Traditionally, door assemblies have been made entirely of wood. The wood provides the necessary strength and rigidity to enable the assembly to maintain its shape, and it gives the assembly a pleasing appearance and feel. However, wooden doors chip, crack, and become weathered. In addition, they are expensive and heavy. To overcome the problems associated with wooden doors, metal exterior doors and composite skin interior doors have been used.
Exterior metal doors with filler materials solve the problems of weathering, cracking, and chipping associated with wooden doors. The metal skin provides the necessary strength and is easily maintained. The interior of the door can be filled with an insulating material such as polyurethane or polystyrene foam to give the door the desired thermal characteristics. Although these doors are a suitable alternative to wooden doors for exterior use, they are not desirable for interior use because of cost and weight. Moldable composite skin doors are often used as an alternative to wooden doors for interior use. Moldable composite skin doors have many advantages over wooden doors. They are generally lighter than wood doors, they do not weather, chip, or crack, and they are easier to clean and maintain.
Interior door assemblies constructed of moldable composite skins are well known in the art. Since the skins lack necessary strength, a spacer, or other filler material is used to provide the door assembly with the necessary rigidity. Generally, the spacer is made of strips of wood or corrugated cardboard that are bonded to the skins. Without the spacer that is bonded to the outer skins, the door assembly would easily deflect. Although the spacer provides rigidity to the door assembly, it also increases the cost and weight of the door assembly and requires a complex manufacturing process.